The present invention relates to a method and to an installation for collecting fresh water from a spring at sea.
The technical sector of the invention is the field of methods and/or installations serving firstly to detect and locate, and secondly to collect fresh water from a spring that emerges into the sea.
The main application of the invention lies in making genuine field for the production of fresh water from springs situated beneath the sea so as to deliver fresh water to populations living in particular in semi-arid zones adjacent to sea basins such as the Mediterranean.
Various methods and apparatuses are already known for collecting fresh water from undersea springs, such as those described in particular in patent application FR 2 701 974 filed on Feb. 26, 1993 which teaches a structure having a downwardly-directed concave side covering such a spring, with the fresh water being trapped in the top portion thereof because its density is lower than that of sea water: the bottom of that structure is open so as to allow sea water to escape and fresh water to penetrate therein. The fresh water is pumped from the top portion of the structure by means of a pumping system installed on the surface, above and vertically over the coastal wall against which said structure is fixed. Such a method and apparatus are particularly adapted to collecting fresh water along coasts but cannot be used for springs situated off-shore at a distance from the coast. Furthermore, before being able to collect fresh water from such springs, it is necessary to identify them and that is more difficult when the springs are out at sea.
The problem posed is to be able initially to identify surface zones beneath which there might exist such fresh water springs gushing from the bottom of the sea, and then to confirm and locate them accurately, and subsequently to install collection apparatus enabling the main part of the flow from such a spring to be recovered without said fresh water becoming polluted with the surrounding sea water and while using implementation means that are simple and easy to install for bringing said fresh water as captured in this way to the shore, even if the spring is far out.
In a first aspect of the solution to the problem posed by the present invention, the present invention provides a method of collecting fresh water at sea, in which:
a first weight is placed close, and preferably as close as possible, to a fresh water resurgence point located on the bottom of the sea, and secondary weights are positioned at given distances relative thereto to form a closed line around the first weight and said fresh water resurgence point;
a flexible reservoir constituted by an envelope suitable for taking up a bell-shape, is lowered in the folded state, preferably furled by means of ties, and weighted at its bottom portion, vertically towards the first weight;
said envelope is deployed by unfolding it and preferably by unfurling it until the circumference of its bottom end is located at a given distance from said secondary weights so that said envelope takes up said bell-shape, preferably in the form of a spherical cap; and
fresh water is collected beneath the flexible reservoir installed in this way.
Said envelope takes up said bell-shape under the pressure of the water that fills it.
In an embodiment, the fresh water can be collected by means of a pump. In which case, said pump can be installed on said first weight and said pump can be put into operation when the level of the, interface between fresh water and sea water is at least below the level of the pump intake, and the fresh water that has been taken in this way is delivered via a delivery pipe.
It is also possible to collect fresh water, with or without a pump, by means of a pipe that opens out at a first end in the top portion of the inside of the reservoir, and at a second end in a zone on land situated below sea level, preferably into a container.
In a first embodiment, a chimney is installed inside said reservoir, the chimney being open at its top portion and surrounding the fresh water resurgence at least in part and preferably in full. The bottom portion of said chimney is preferably secured in leakproof manner to the bottom of the sea. After an initial period of evacuating sea water, this leakproofing makes it possible to prevent the flow of fresh water coming into contact with sea water while the fresh water is rising into the top portion of the inside of the reservoir.
In this embodiment with an internal chimney, it is not essential for the bottom end of the reservoir to be secured in leakproof manner to the bottom of the sea, so the reservoir can be spaced apart from the bottom of the sea.
In another embodiment, after the envelope has been deployed and until the bottom circumference thereof has been put into position at a given distance from said secondary weights so as to cause it to take up said bell-shape, the bottom end of the reservoir is secured to the bottom of the sea in leakproof manner. In this embodiment, the secondary weights make it possible to take up forces so as to move the bottom end of the reservoir as close as possible to the bottom of the sea, thereby making it possible to establish a leakproof connection. In this embodiment, it is not essential to install said chimney inside the reservoir.
Said chimney and/or said reservoir can be secured in leakproof manner to the bottom of the sea by causing the circumference of the bottom end of said chimney or said reservoir to fit closely over the relief of the bottom of the sea.
In the present invention, the term xe2x80x9cleakproofingxe2x80x9d is used to mean that contact is prevented between the water inside the reservoir or the chimney and the water outside. The leakproofing can be total or merely substantial so as to ensure that no significant mixing takes place, thereby providing fresh water that is not significantly mixed with the sea water on the outside.
In an embodiment, said flexible reservoir is constituted by a double-walled envelope that is preferably subdivided into compartments, into which a slurry of concrete is injected, which concrete preferably has specific gravity close to 1, and is injected after the envelope has been deployed, and preferably after leakproofing has been established between the circumference at the bottom end of the reservoir and the bottom of the sea, when the reservoir has taken up said bell-shape under the pressure of fresh water filling it.
Preferably, when the flexible reservoir constituted by an envelope suitable for taking up a bell-shape is lowered, the top portion of said envelope, which remains open, is surmounted by a float, and when said envelope is deployed so as to adopt said bell-shape, the top portion of the bell is closed by an escape valve for allowing any gas that may be contained in the fresh water to escape, and the fresh water is collected from the underside of the flexible reservoir as installed in this way.
More particularly, when said flexible reservoir constituted by an envelope is lowered in furled form vertically towards the first weight, sling lines are fixed between each secondary weight and the circumference of the bottom end of the bell, and the bell is unfurled by pulling on said lines until said circumference of the bottom end is positioned at a given distance from said secondary weights such that the envelope takes up said bell-shape, preferably in the form of a spherical cap, and preferably a hemispherical cap.
The present invention also provides an installation for collecting fresh water that is resurgent at sea, the installation comprising an immersed bell-shaped reservoir, preferably in the form of a spherical cap, with its open concave side facing downwards, and suitable for trapping fresh water in its top portion, and a system suitable for taking said fresh water, the installation being characterized in that the circumference of the bottom end of said reservoir and/or the circumference of the bottom end of a chimney inside said reservoir and open at its top end and surrounding the fresh water resurgence in part and preferably in full, follow(s) closely the outline of the relief of the bottom of the sea so as to provide leakproofing between said circumference(s) and the bottom of the sea.
In an embodiment, the installation includes one of said chimneys inside said reservoir, the chimney being open at its top portion and surrounding the fresh water resurgence at least in part and preferably in full, the circumference of the bottom end of said chimney fitting closely to the outline of the relief of the bottom of the sea in such a manner as to provide leakproofing at the bottom of the sea, and the circumference of the bottom end of said reservoir being spaced apart from the bottom of the sea.
In another embodiment, the installation comprises a reservoir constituted by a double-walled envelope, that is preferably subdivided into compartments, into which there is injected a slurry of concrete of specific gravity preferably close to 1, the circumference constituting the bottom end of the reservoir being secured to the bottom of the sea in leakproof manner, and said installation not having said internal chimney.
In a second aspect of the invention, a solution to the problem posed is a method of detecting, locating, and collecting fresh water at sea in which the fresh water resurgence point is detected and located by performing the following steps:
at least the salinity of the sea water is measured at various points in a zone where it is believed that there is a reasonable chance of finding a fresh water resurgence point under the sea; and
if a difference is obtained between at least one of said salinity values and the value for sea water situated outside said zone, and if said difference is greater than a given threshold, it is deduced that the bottom of the sea corresponding to said zone and in the vicinity of the point at which the different salinity measurement was taken includes at least one fresh water resurgence point, the method being characterized in that a chart of salinity for all of said zone is drawn up using a number of measurement points that is sufficient to enable iso-salinity curves to be plotted, and potential fresh water resurgence points are determined as lying at the centers of curves corresponding to the greatest salinity anomalies, said measurement points preferably being taken from the surface, and more preferably still at a substantially constant depth of immersion, preferably by towing a salinity probe from a vessel.
Once such a spring has been detected and located, it is then possible to implement the steps of the method of the invention to enable the fresh water to be collected, as explained above.
The invention thus provides novel methods of detecting, locating, and collecting fresh water from springs at sea, together with corresponding installations, that resolve effectively the problem posed and enable fresh water to be pumped quite safely, even in the event of gas contained in the fresh water being produced simultaneously, and that is not possible with the apparatus disclosed in the above-cited patent, with this making it possible to work undersea resurgences of fresh water on an industrial scale. The present invention should thus make it possible to reduce shortages of fresh water in countries such as those of the Mediterranean basin, thereby contributing to the development thereof. It is known that fresh water resurgences of karstic origin exist around the Mediterranean: on its own, Greece has reserves that would enable an annual production of fresh water that is estimated at about 2.5 billion cubic meters, and other Mediterranean countries, including France, have fresh water resources of this type in their territorial waters. Given the depletion of natural fresh water resources, and the increase in consumption, and thus the increase in price, the present invention should make it possible to satisfy the needs of the countries concerned.
Other advantages of the present invention could be mentioned but those given above suffice to demonstrate the novelty and the advantage of the invention.